Polyphenylene ethers have excellent transparency, mechanical and electrical properties, heat resistance and dimensional stability as well as advantageously low moisture absorption. However, polyphenylene ethers have poor moldability and poor impact strength.
To obviate the drawbacks of poor moldability and poor impact strength, it has been attempted to blend a polyphenylene ether with a polystyrene or a high impact polystyrene. Compositions comprising a polyphenylene ether and a polystyrene or a high impact polystyrene are now widely used to manufacture electrical and electronic components, housings for business machines, automobile parts, precision components and other engineering materials. With respect to such classical polyphenylene ether resin compositions comprising a polyphenylene ether and a high impact polystyrene, reference is made to, for example, U.S. Pat. No. 3,383,435. Such polyphenylene ether resin compositions exhibit improved impact strength. However, they have poor chemical resistance.
Proposals for improving both of impact strength and chemical resistance, especially solvent resistance, by blending a polyphenylene ether with a polyolefin have been made, for which reference is made to, for example, U.S. Pat. No. 3,361,851 and Japanese Examined Patent Application Publication Specification No. 42-7069/1967. Compositions comprising a polyphenylene ether and a polyolefin suffer from severe delamination so that the actual application of the compositions is extremely limited.
In the art, other various proposals have also been made. U.S. Pat. No.3,994,856 discloses a composition obtained by blending a polyphenylene ether or a combination of a polyphenylene ether and a polystyrene resin with a hydrogenated block copolymer, which composition is described as exhibiting improved impact resistance and solvent resistance. Further, U.S. Pat. No. 4,145,377 discloses a composition comprising a polyphenylene ether or a combination of a polyphenylene ether resin and a polystyrene resin, a preliminary blend of a polyolefin and a hydrogenated block copolymer in weight proportions of 20-80: 80-20, and a hydrogenated block copolymer, which composition is described as exhibiting improved impact resistance and solvent resistance. Still further, U.S. Pat. Nos. 4,166,055; 4,239,673 and 4,242,263, disclose compositions obtained by blending a polyphenylene ether with a block copolymer or with a combination of a hydrogenated block copolymer and a polyolefin, which compositions are described as having improved impact resistance. Still further, U.S. Pat. No. 4,383,082, European Patent Publication No. 115,712 and Dutch Patent No. 7,410,861 disclose compositions obtained by blending a polyphenylene ether with a polyolefin and a hydrogenated bock copolymer, which compositions are described as having improved impact resistance. Still further, U.S. Pat. No. 4,863,997 and Japanese Patent Application Laid-Open Specifications Nos. 63-113058/1988; 63-225642/1988; 64-98647/1989; 64-204939/1989 and 64-221444/1989 disclose compositions obtained by adding a specific hydrogenated block copolymer to a blend comprising a polyolefin resin and a polyphenylene ether resin, which compositions are described as having improved chemical resistance and moldability. Still further, Japanese Patent Application Laid-Open Specification Nos. 63-218748/1988; 63-245453/1988 and 64-40556/1989 disclose compositions obtained by melt kneading a precompound comprising a specific block copolymer and a polyolefin with a polyphenylene ether, which compositions are described as having improved chemical resistance and moldability. The above-mentioned various polyphenylene ether resin compositions exhibit improved solvent resistance and impact resistance as compared to the conventional polyphenylene ether resin composition comprising a polyphenylene ether and polystyrene or a high impact polystyrene. However, they have inherent problems which limit their applications. In particular, conventional compositions comprising at least 50% by weight of a polyphenylene ether and up to 20% by weight of a polyolefin result in a shaped article which exhibits severe delamination and poor weld-line toughness. Such compositions cannot cope with an increasing demand for higher quality in the art with respect to engineering plastics.